Stack quad adapter woes

[kurja]

Is anyone else having trouble with stack quad adapters? I made a rocket with an orange tank midsection and four orange tanks as boosters, all of them with quad adapters, boosters with four lv-t30s each and four lv-t45s on the center, and it won't go to space. At all. Most launches fail because a couple lv30s just plop off when still sitting on the launchpad, and when that doesn't happen, the whole center adapter with all of it's engines comes off of it's fuel tank, after having throttled down waiting for circularization at apokee.

Probably unrelated to adapters, but the rocket has >1.5 twr just with the boosters and it won't lift off. Won't budge at all, unless I fire up the center stage as well. As if the center engines were glued to the pad.

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

[rottielover]

Questions. So you are not using launch clamps? (Engines sitting directly on the pad with all that weight on them?). What about struts?

Isn't the TWR calculated based on the staging? If its calculated based on all the engines but your deactivating some that would make your TWR drop.

Can you put a pic?

[LameLefty]

... the whole center adapter with all of it's engines comes off of it's fuel tank, after having throttled down waiting for circularization at apogee.

I've had that happen to me with a robotic fuel tanker design I use sometimes that has four engines on the final core lifter. If I let Mechjeb fly the ascent, it happens almost every time. If I hand-fly it, no problem. I solved the problem by putting on 4 or 6 struts between the quad-adapter and the core tank.

[kurja]

Questions. So you are not using launch clamps? (Engines sitting directly on the pad with all that weight on them?). What about struts?

Isn't the TWR calculated based on the staging? If its calculated based on all the engines but your deactivating some that would make your TWR drop.

Can you put a pic?

I used clamps, and the boosters were off the ground. Engines seem to just drop off at random. Struts help of course but the node between adapter and engine really should be able to take the weight on it's own, it's just one lv-t30 after all, just hanging there. And -plop-

Center engines are on a different stage, the twr reading should be correct.

I can up a picture a little later.

[kurja]

Here's a picture - right off the pad, you can see a couple engines missing.

hmm Lamelefty, I were using mechjeb here, too, maybe it has something to do with it, I can't see how though.... but I'll try. Engines fall off on the pad, when MJ isn't doing anything yet.

[kurja]

hmm, the center indeed did not fall off when ascending manually... curious

[FITorion]

a bug caused by a Mod? say it ain't so.

kidding. kidding. Mechjeb always blows up my rockets though. Or at least it did and I very quickly stopped using it.

[GoDores]

I've had the issue with engines randomly falling off the bottom of quad adapters, even when I used launch clamps. I'm not sure why it happened and I never was able to solve it. I had to give up on the design since it wouldn't fly straight with the missing engines. I think the issue is that connection strength doesn't seem to scale up with part size; compact landers and probes can survive impacts that would destroy any real ship, but large rockets fall apart like wet tissue paper even when they appear to be solidly constructed and thoroughly strutted. I'm sure the issue is being worked on for future updates.

I've also had my final stage engines get ejected when using Mechjeb. It happens if MJ is allowed to auto-warp; it will go to 4x physics warp while in the atmosphere waiting to get to apoapsis, which invariably causes my orbital insertion stage to shake off its engines and become quite useless. If I disable auto-warp, I don't have the problem. I've gone back to just flying launches manually since I can launch to rendezvous better than MJ seems to be able to.

[dizzysaurus]

Lock gimbals and make sure you have linked the 4 tanks using struts.

[Moar Boosters]

I think it might be a throttle control issue as well. Increase power slowly and it puts a lot less strain on the engines. Mechjeb tends to use the throttle as an on/off switch so it'll often break rockets that fly fine manually as long as you're gentle with the throttle.

[King Arthur]

The short answer is you need more struts. I always make sure to thoroughly strut my launch vehicles and I've never had them RUD themselves under both manual and MechJeb control. My current heavy launcher which has a max payload of ~80t to 75km*75km LKO (standard 40~60 to 150km*150km LKO) even has a perfect safety record, not a single failed launch to date.

[roosterr]

I have seen this problem. If you put struts, fuel lines, winglets or any other parts that "clip" into the engine section they explode shortly after launch. "Falling off" may be a different problem, but I have seen mine go "poof" and blow up. Remove all parts that may be touching the engines and see what happens.

[kurja]

people,

there's nothing clipping or touching the booster engines (unless there's a well hidden strut somewhere in there), and they are under no stress other than their own weight when they come off at the pad.

No lift-off was fixed by raising the craft on the clamps just high enough to get the center clear of the pad.

When the center engines come off, the ship is coasting in freefall to apoapsis >60km above kerbin. Apparently this only happens if mechjeb is active, I can't see how mj could cause this but that's how it seems.

Such things could be helped with struts but really!? Well I ultimately managed a launch with all engines on as long as needed.

[CoriW]

Well that's strange, all of my new lifters use Quad Adapters with LV-T30's for the boosters and it's worked perfectly every time. However I completely avoid using the Rockomax Jumbo-64 Fuel Tanks and always use the the Rockomax X200-32 Fuel Tanks instead because of previous overheating issues I've had, not sure if maybe that's what's causing your problem or if it actually is something to do with MechJeb?

I also have MechJeb, but all I use from it is the Smart A.S.S. so I'm not sure if that would be the problem or not, I don't think that it would be an issue with throttling up to 100% at once though because most of my launches ignite the engines at 100% thrust. So in conclusion the only possible issue I can think of is the use of a Rockomax Jumbo-64 Fuel Tank causing the engine to fall off, although that does seem unlikely because the engine is falling off the quad coupler and not the fuel tank itself.

Still, might be worth a try to swap out the current fuel tanks for Rockomax X200-32 Fuel Tanks and see if the issue persists.

[Galane]

I tried a simple rocket with one orange tank with a mainsail on the bottom for the second stage and four solids for the first stage. Nothing else but a nosecone and an RGU. It'd leave the mainsail on the pad, just fall right off when the solids light up.

Kerbals must either buy their bolts from the supplier who undercut the lowest bidder or perhaps it's... http://www.spaceflightnow.com/news/n0410/04noaanreport/

[DocLangy]

Question, when you placed the engines in the VAB did you use symmetry? Could that maybe be causing the issue.

[Galane]

Symmetry to place the separators and the solid boosters.

[Rufus Callahan]

you should crossfeed and ignite all of the engines at launch.

[JakeGrey]

So far as I know, the overheating issue only happens when you attach a Mainsail -or presumably any other 2.5m engine- directly to the bottom of a Jumbo-64; they've got some kind of issue with getting rid of waste heat. Using one bof those multi-way adapters should prevent that, I think, but I can't say I've ever tried it myself.

[Galane]

Yeah, problem with that is four of the highest thrust engines that fit the quad adapter don't have the power of one mainsail. I found that out early on in my testing on the Big Light Booster, which ain't so light anymore.

Launch and, oh, hey, the rocket is kinda skidding sideways while slowly tipping over. I have three test rockets (which I'll have to look at to see their configuration) with the same engine configuration and different ways of crossfeeding the fuel among them. Turned out that what got the highest altitude was (IIRC) letting the four side mounted engines vampire from the central 64 tank then dropping the mainsail engine to shed its weight. Feeding fuel the other way then dropping the side engines or feeding both ways so all five engines ran out at the same time got less altitude straight up at burnout.

That's where I ran into leaving the mainsail on the pad, the kick from lighting up the side engines with a stack separator (no fuel crossfeed option, boooo!) between the big engine and the tank would knock it loose. Piping fuel over a stack separator to an engine directly attached to the separator (apparently with the Kerbin version of blu-tack) can't be done directly for some reason. The end of the pipe refuses to cross over and stick to the engine. I had to resort to sticking a Small Hardpoint to the separator then run a fuel pipe to the hardpoint and another from the hardpoint to the engine.

Tada! A staged engine dropper. I don't even want to guess at what MechJeb would do with it.

[magnemoe]

I think it might be a throttle control issue as well. Increase power slowly and it puts a lot less strain on the engines. Mechjeb tends to use the throttle as an on/off switch so it'll often break rockets that fly fine manually as long as you're gentle with the throttle.

True, mechjeb accent autopilot can also be used in manual mode to give flight path indication and warn then reaching terminal speed.